MKUHIAM: TH1ASSIC [CHTHYOSAUEIA. Ill 



the coronoid region a plate-like element occupying the position of the coronoid. 



This element extends l)ack\vard from its normal position, passing bel \vcen the 

 inner plate of the angular and the inner side of the articular, and falling but 

 a little short of reaching the extreme posterior end of the jaw. In a specimen 

 of B((i>t<uto<l<m (no. 878) at the Carnegie 'Museum in Pittsburg the same rela- 

 tions of these elements have been noted, and the coronoid extends quite to the 

 posterior end of the ja\v."' ; 



The articular of Cymbospondylus i>cl riimx rises abruptly behind the eotylus 

 where the thickened anterior end forms a heavy posterior buttress against 

 which the quadrate articulates posteriorly. It extends backward to the poste- 

 rior end of the jaw, where it is again considerably thickened. On all of the 

 specimens that have been examined, the posterior portion is deeply excavated 

 superiorly between the anterior and posterior thickened regions. 



Dentition. In general, the characters of the dentition of Cymbo8pondylus 

 excepting the insertion are essentially similar to those of Ichthyosaurus. Both 

 upper and lower jaws are set with conical teeth numbering from thirty to 

 thirty-five for each ramus of the jaw. In some cases at least (figs. 10 to 12), 

 the teeth are situated in completely enclosed bone pits. Though the ante- 

 rior teeth seem to have somewhat more slender crowns than the most posterior 

 ones there appears to be no close approach to the degree of differentiation seen 

 in Mi.roxiiin-nx. The amount of cement on the roots of the teeth seems to be 

 small. The dentine is strongly folded toward the base. The enamel of the 

 crown is finely but sharply striated. 



MEASUREMENTS OF SKULL OF C. petrinus, NO 9950. 



Greatest length of skull on horizontal plane .................................................................. 1166 mm. 



Length, anterior end of premaxillary to posterior border of pineal 



foramen ............................................................................................................................ 814 



Length, anterior end of premaxillary to anterior border of left orbit ... 717 



Length. anterior end of premaxillary to anterior end of maxillary ......... 373 



Greatest height of skull ....................................................................................................... 365 



Premaxillary, anteroposterior diameter .............................................. 650 



Anterior end of nasals to anterior border of pineal foramen ........................ 380 



Supratemporal fenestra, anteroposterior diameter ................................. 190 



Lateral temporal bar, anteroposterior diameter .......................................... 160 



Orbit, anteroposterior diameter ...................................... 



Orbit, height ................................................................................. 115 



Length of right ramus of mandible ................................... 



Mandible, height below middle of orbit .................. 114 



VcrtchniJ ColioHii. The most nearly complete specimen which has been ex- 

 amined (no. 9950) shows a practically complete vertebral series back to the 



-a Gilmore, C. W., Mem. Carneg. Mus., vol. 2, pp. 97 and 98, and pi. 11, fig. 2. 



